Enantiomerically pure polymers are valuable due to their optically active properties for uses ranging from materials science to synthetic organic chemistry. These polymers can be prepared by the polymerization of enantiomerically pure monomers. However, most enantiomerically pure monomers are difficult and/or expensive to prepare compared to their racemic counterparts, such that polymerization of enantiometically pure monomers is not a realistic option.
Some efforts have been made to develop enantioselective methods for preparing enantiomerically pure polymers. Specifically, Furukawa and co-workers (Tsuruta, Teiji; Inoue, Shohei; Yoshida, Norimasa; Furukawa, Junji., Makromolekulare Chemie (1962), 55, 230-1; Inoue, Shohei; Tsuruta, Teiji; Furukawa, Junji., Makromol (1962), 215-18) have described the enantioselective polymerization of racemic propylene oxide (PO) with catalysts consisting of ZnEt2 and enantiomerically pure alcohols such as (+)-borneol. This system produces optically active crystalline poly(PO) and enantio-enriched PO with a selectivity factor (krel=kfast/kslow) of 1.5. Since this discovery, numerous combinations of alkyl metals and chiral alcohols have been evaluated for the enantioselective polymerization of PO. However, no catalyst has been identified that demonstrates high enantioselectivity in this reaction.